Problem: Michael is $4$ times as old as Brandon and is also $27$ years older than Brandon. How old is Brandon?
We can use the given information to write down two equations that describe the ages of Michael and Brandon. Let Michael's current age be $m$ and Brandon's current age be $b$. Let Michael's current age be $m$ and Brandon's current age be $b$. ${m = 4b}$ ${m = b + 27}$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $b$, and both of our equations have $m$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 = {4b} -{(b + 27)}$ which combines the information about $b$ from both of our original equations. Solving for $b$, we get: $3 b = 27$. $b = 9$.